RectLight Scaling

[aweidenhammer]

release Aug build

Scaling a light in the viewport (transform scaling) has some unintended consequences. I think scaling the light is scaling the diffuse and reflection contributions of the light more than it does when you use the lights U and V size. For example. When you set a light to "Lumens", the scale of the light should not affect its intensity. But it does. Things get uncontrollably bright when scaled up by say 50 or 100 in the X,Y. I set to 1500 lumens, and the scale of the light indeed goes much brighter. This is also the case when using a texture on the light, and has some even stranger reactions there...

Scaled via transforms and not UVsize; using a texture on the rectLight; shining on a glossy chrome material, the reflections are very strange. Inverted? Use about a .85 for reflGloss.

I didn't pack up a scene, since it's pretty easy to reproduce. Let me know if you need one tho.

[snivlem]

I've always wondered which is the correct way to resize a light? Via scale or U+V size.

[aweidenhammer]

So here are some example images. Sphere, and rectLight. First, no texture on the light. The settings are basically a sphere with about half reflective color, and no fresnel. gloss=1 The area light is scaled to 50x50 and placed about 70 units away. The light units are set to Lumens = 1500.

The first image is where the light's xformScale = 1 and the UV sizes are set to 50. Looks correct. The second image has UV set to 1 and the xformScale = 50. That would be very wrong, and takes a sick amount of time to render for sampling such bright values.



The next set is the same except an hdr texture of a softbox has been placed onto the light.



Again, the UV scaling is used in the first image, and the result is correct. The second image transform scaling is used and the image is totally blown out. so bright it is practically unrecoverable, and obviously results in long rendertimes and poor sampling as well.

This issue seems to still be in recent builds, as this is from build April26, 2010

[vlado]

Scaling the light will produce incorrect results currently. I'll make a note to correct this.

Best regards,
Vlado

[aweidenhammer]

I should point out here, that using Lumens could be the source of the oddity, so I tested default units, which most people probably use most often (Intensity=1). When not using textures on the lights, the behavior seems correct when scaled with UV or XY. So I won't post images. But when using a texture (same hdr as above) there are bugs with the diffuse component. some images to illustrate:

First image with a texture, the light is scaled via UV. This looks good.


Second image the scaling is in the XY and UV set to 1. Where did my diffuse go?

[aweidenhammer]

This is a bit of a problematic fix, when you think about it. Code-wise, perhaps not difficult (I have no idea)... but practically, it will change lighting for all scenes previous that used transform scaling... which I assume is most peoples' scenes. Though I haven't tested every possible option, I think that non-textured lights set to "default" units will not have a problem, so that may result in a large chunk that will be unaffected. Though who am I to assume what most people use? Guess I'll stop thinking out loud now.

BTW, I built a lighting rig internally here that for now, pipes scaling into the UVsize, and inverses the transform scale, to keep it at 1. That way, you can scale all you want in the viewport, and forget about your troubles If anyone is interested, I'll post it, but not all that bid a deal to build yourself.

[Metzger]

I think if the rectangle lights can be properly scaled, then the U and V size should be disabled if scaled.. Not sure if it can be done. It should be one or the other. Much easier to scale the light than to input u and v size.

[sersia]

Any Update for this???

[vlado]

For which part? Scaled lights should behave a lot better now (identical to non-scaled lights), but I would still recommend to use the U/V size instead of scaling.

Best regards,
Vlado

[sersia]

Could we have an option to keep the intensity when we change the unit from default to the others even if we change the transform scale of vraylightrect instead of u, v size?
Please check the image file attached, just for your information.

[thescopeteam]

For which part? Scaled lights should behave a lot better now (identical to non-scaled lights), but I would still recommend to use the U/V size instead of scaling.

Best regards,
Vlado

Hey, Vlado, does the issue still exist in Vray Next 4.3 ? I can not see or measure any differences between a scaled light and a light with the same scale in UV

[SonyBoy]

Seems like a good time to ask what is the rationale behind the U and V parameters on rect lights. I'm sure I'm not alone in finding it significantly more user friendly and intuitive to simply scale lights in the same way anything else is scaled, rather than have to mess about with sliders or values in the attribute editor.

[Morbid Angel]

Yeah I'm not a fan of UV sliders esp in maya they are limited in channel box to like 10x10 and you cannot click/drag the value past that, I've reported this before but it never got fixed.

[Karol.Osinski]

SonyBoy I believe it's keep the right placement of the light texture if you use one. I remember applying the softbox texture to the rect light and direct scaling broke it while scaling the light with its own parameters kept the texture in right position.

[SonyBoy]

Still not sure what the advantage of UV scaling versus transform scaling is in regards to texture -- the end result appears exactly the same. What you're saying would make sense if UV scaling worked independently from image placement in the light's UV space (i.e. the image would "slide" over the light's surface area during scaling), but it doesn't. Furthermore, rect lights themselves don't actually have any editable UVs. So, to my uneducated eyes, the UV scaling feature seems to be completely redundant and just an annoyance to users.